Why bones IK change positions by itself?
When an IK chain change position in weird ways, it's because of one of this problems:


the ik traget location is modified by the movements of one bone of the chain itself: so there is an endless circularity. Check if it has constraints related to any bone of the chain, or if it is child of a bone related to the chain.
some bends have a flipped position that can resolve the IK request, so you need to establish a pole target to have full control of the behaviour of the chain